critical CVSS 9.1

CVE-2026-64393·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: ksmbd: run set info with opener credentials SMB2 SET_INFO handlers call path-based VFS helpers after checking the access mask granted to the SMB handle. Those helpers perform their owner, inode permission and LSM checks using the current ksmbd worker credentials. Run the complete SET_INFO dispatch with the credentials captured when the handle was opened. This also removes the separate security information credential setup and keeps all SET_INFO classes under one credential scope. Direct override_creds() is used because it can nest with the request credential overrides already used by rename and link helpers.

Severity
critical
Software
Kernel
Fixed in
7.1.4
Published
2026-07-25

Affected versions

From: 6.19

Until: 7.1.4

Fixed in: 7.1.4

How to fix this CVE

Update your Linux kernel to version 7.1.4 or later to resolve a critical privilege escalation vulnerability in the ksmbd SMB server component. The vulnerability allows authenticated attackers to bypass access control checks by exploiting improper credential handling during SET_INFO operations. Ensure all systems running kernel versions 6.19 through 7.1.3 are patched immediately.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check installed kernel version with `uname -r` and compare against affected range (6.19 to 7.1.3)
  2. Step 2: Verify ksmbd is enabled by checking `grep -i ksmbd /boot/config-$(uname -r)` for CONFIG_SMB_SERVER=y
  3. Step 3: Monitor /var/log/audit/audit.log for denied capability checks or permission violations on SMB file operations using `grep -i 'denied.*cap.*dac' /var/log/audit/audit.log`
  4. Step 4: After patching, confirm kernel version with `uname -r` returns 7.1.4 or later and reboot to activate changes

FAQ

What is CVE-2026-64393?

This is a privilege escalation vulnerability in Linux kernel's ksmbd SMB server where SET_INFO operations execute with incorrect security credentials, allowing attackers to modify files or attributes they should not have access to. The flaw stems from using worker thread credentials instead of the opener's credentials when performing permission checks.

Is CVE-2026-64393 being actively exploited?

No, this vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities catalog, and no public exploits are available at this time.

What versions of Kernel are affected by CVE-2026-64393?

Linux kernel versions 6.19 through 7.1.3 are vulnerable. Version 7.1.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-64393?

Run `uname -r` to check your kernel version; if it shows 6.19 to 7.1.3 and ksmbd is enabled (check with `grep CONFIG_SMB_SERVER /boot/config-$(uname -r)`), your system is vulnerable.

Does Defensia detect CVE-2026-64393?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2026-64393 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-64000CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: hsr: fix potential OOB access in supervision frame handling Ensure the entire TLV header is linearized before access by adding sizeof(struct hsr_sup_tlv) to the pskb_may_pull() calls. Without this, a truncated frame could cause an out-of-bounds access.
CVE-2026-64033CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: RDMA/rtrs: Fix use-after-free in path file creation cleanup In the error path of rtrs_srv_create_path_files(), the sysfs root folders may already have been created and srv_path->kobj may already have been initialized. If a later step fails, the cleanup currently calls kobject_put(&srv_path->kobj) before rtrs_srv_destroy_once_sysfs_root_folders(srv_path). kobject_put() may drop the last reference to srv_path->kobj and invoke the release callback, rtrs_srv_release(), which frees srv_path. The following call to rtrs_srv_destroy_once_sysfs_root_folders(srv_path) then dereferences srv_path internally to access srv_path->srv, resulting in a use-after-free. This failure path is reached before rtrs_srv_create_path_files() returns success, so the successful-path lifetime handling is not involved. Fix this by destroying the sysfs root folders before calling kobject_put(&srv_path->kobj), so srv_path is still valid while the helper accesses it. This issue was found by a static analysis tool I am developing.
CVE-2026-64007CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfilter: synproxy: refresh tcphdr after skb_ensure_writable synproxy_tstamp_adjust() rewrites the TCP timestamp option in place and then patches the TCP checksum via inet_proto_csum_replace4() on the caller-supplied tcphdr pointer. Both ipv4_synproxy_hook() and ipv6_synproxy_hook() obtain that pointer with skb_header_pointer() before calling in, so it may either alias skb->head directly or point at the caller's on-stack _tcph buffer. Between obtaining the pointer and using it, the function calls skb_ensure_writable(skb, optend), which on a cloned or non-linear skb invokes pskb_expand_head() and frees the old skb->head. After that point the cached th is stale: caller (ipv[46]_synproxy_hook) th = skb_header_pointer(skb, ..., &_tcph) synproxy_tstamp_adjust(skb, protoff, th, ...) skb_ensure_writable(skb, optend) pskb_expand_head() /* kfree(old skb->head) */ ... inet_proto_csum_replace4(&th->check, ...) /* writes into freed head, or into the caller's stack copy leaving the on-wire checksum stale */ The option bytes are written through skb->data and are fine; only the checksum update goes through th and so lands in the wrong place. The result is either a write into freed slab memory or a packet leaving with a checksum that does not match its payload. Fix by re-deriving th from skb->data + protoff immediately after skb_ensure_writable() succeeds, so the subsequent checksum update targets the linear, writable header.
CVE-2026-64025CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: bpf, skmsg: fix verdict sk_data_ready racing with ktls rx sk_psock_strp_data_ready() already checks tls_sw_has_ctx_rx() and defers to psock->saved_data_ready when a TLS RX context is present, avoiding a conflict with the TLS strparser's ownership of the receive queue (commit e91de6afa81c, "bpf: Fix running sk_skb program types with ktls"). sk_psock_verdict_data_ready() has no equivalent guard. When a socket is inserted into a sockmap (BPF_SK_SKB_VERDICT) before TLS RX is configured, tls_sw_strparser_arm() saves sk_psock_verdict_data_ready as rx_ctx->saved_data_ready. On data arrival: tls_data_ready -> tls_strp_data_ready -> tls_rx_msg_ready -> saved_data_ready() = sk_psock_verdict_data_ready() -> tcp_read_skb() drains sk_receive_queue via __skb_unlink() without calling tcp_eat_skb(), so copied_seq is not advanced. tls_strp_msg_load() then finds tcp_inq() >= full_len (stale), calls tcp_recv_skb() on the now-empty queue, hits WARN_ON_ONCE(!first), and returns with rx_ctx->strp.anchor.frag_list pointing at a psock-owned (potentially freed) skb. tls_decrypt_sg() subsequently walks that frag_list: use-after-free. Apply the same fix as sk_psock_strp_data_ready(): if a TLS RX context is present, call psock->saved_data_ready (sock_def_readable) to wake recv() waiters and return immediately, leaving the receive queue untouched. TLS retains sole ownership of the queue and decrypts the record normally through tls_sw_recvmsg().
CVE-2026-100075CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: RDMA/srpt: Fix srpt_alloc_rw_ctxs() unwind counters When srpt_alloc_rw_ctxs() fails partway through a multi-buffer indirect descriptor, the unwind path destroys RDMA contexts but leaves stale n_rw_ctx and n_rdma values (and a dangling rw_ctxs pointer). Later sq_wr_avail accounting in srpt_queue_response() or srpt_write_pending() can then subtract the wrong number of send queue credits. Reset the counters and clear rw_ctxs after freeing the heap allocation before returning an error.

References

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